How Big Does a Si Nanocluster Favor Bulk Bonding Geometry?

Low-energy structures of silicon nanoclusters (NCs) at the size about 220 atoms were studied using tight-binding and first-principles calculations. The structures including bulk-like, icosahedral, bucky–diamond, and onion-like structures have been extensively investigated. The results showed that the bulk-like structures are energetically favorable for the Si<sub>220</sub> NCs. Our calculations also showed that although the icosahedral structure is energetically competitive with the bulk-like structures at the special size of 220 atoms, the bulk-like structures are more robust as the number of atoms varies. We also studied the structure-energy trend for Si NCs as the function of cluster size and the structural transition to bulk-like motif occur at the size range of 173–215 atoms.